Barrier Corona Research Articles

Average OH density in alternating current dielectric barrier discharge by laser-induced fluorescence technique

The average OH density in atmospheric He–H2O(0.4%) needle-plate dielectric barrier discharge (DBD) was measured by the asynchronous laser-induced fluorescence (LIF) technique and the fluctuation of OH radical density was measured simultaneously to prove that the average OH density can be obtained by the asynchronous LIF technique. The evolution of the average OH density in four different discharge patterns, namely, negative barrier corona discharge, glow discharge, multi glow discharge, and streamer discharge, was studied, and it was found that the average OH density has an observable increase from corona discharge to streamer discharge. The main mechanism of OH production in the four different discharge patterns was analyzed. It was shown that the main mechanism of OH production in negative barrier corona discharge is electron direct collision dissociation, whereas in the other three discharge patterns the He metastable Penning ionization is the main process.

Inactivation Effect of Low-Temperature Plasma on <italic>Pseudomonas aeruginosa</italic> for Nosocomial Anti-Infection

Disinfection and sterilization in hospitals and other public places have always been the focus of attention. In our studies, dielectric barrier corona discharge (DBCD) was used to generate low-temperature plasma (LTP) to treat Pseudomonas aeruginosa ( P. aeruginosa , one kind of bacteria responsible for nosocomial infections). The survival colonies of P. aeruginosa were counted with the standard plate-counting method after 30-, 60-, 90-, and 120-s exposures to DBCD. We discovered that LTP could lead to more than 5-log reduction of P. aeruginosa after 120-s treatment. Further experiments indicated that OH and excited N2 in LTP and lower pH value in bacterial suspension might synergistically inactivate P. aeruginosa by destroying its outer structure.

Plasmachemical synthesis in low-temperature atmospheric pressure plasma

Pesicular features of various types of electrical gaseous discharges used to generate and sustain low-temperature plasma at atmospheric pressure have been considered. Applications of dielectric barrier discharges (DBD), corona, radiofrequency (RF), and microwave (MW) discharges for the synthesis of different materials have been discussed.

Measurement of ion density in an atmospheric pressure argon with pin-to-plate dielectric barrier discharge by resonance of plasma radiation

The measurements of the ion densities in the atmospheric AC barrier corona argon discharge are carried out by receiving and analyzing the frequencies of the electromagnetic radiation emitted from the plasma. An auxiliary excitation source composed of a pin-to-pin discharge system is introduced to excite the oscillations of the main discharge. To analyze the resonance mechanism, a complemented model based on a one-dimensional description of forced vibrations is given. Calculations indicate that Ar2+ is the dominant ion (∼89% in number density). By analyzing resonance frequencies, the ion densities of Ar2+ are in the order of 1019∼1020m−3 and increase slowly as the applied voltage increases.

Instability wave control in turbulent jet by plasma actuators

Instability waves in the shear layer of turbulent jets are known to be a significant source of jet noise, which makes their suppression important for the aviation industry. In this study we apply plasma actuators in order to control instability waves in the shear layer of a turbulent air jet at atmospheric pressure. Three types of plasma actuators are studied: high-frequency dielectric barrier discharge, slipping surface discharge, and surface barrier corona discharge. Particle image velocimetry measurements of the shear layer demonstrate that the plasma actuators have control authority over instability waves and effectively suppress the instability waves artificially generated in the shear layer. It makes these actuators promising for application in active control systems for jet noise mitigation.

Analysis and design of pulse frequency modulation discontinuous‐current‐mode dielectric barrier corona discharge with constant applied electrode voltage

In dielectric barrier corona discharge (DBCD) used in material surface treatment, how to obtain a constant peak applied electrode voltage when regulating the power is an important issue as the voltage considerably influences the discharge stability and characteristics. In this study discontinuous current mode (DCM) is used in DBCD for surface treatment. The peak applied electrode voltage is constant when the output power is regulated with pulse frequency modulation, which is simpler than conventional control schemes. Moreover, the power regulation is linear with the operating frequency. Thus, the close-loop design is much easier. Moreover, zero-current-switch turn-on and zero-voltage-zero-current-switch turn-off are achieved with a high frequency and power density. The time-domain analysis is simple in DCM and the expressions for key parameters, in terms of the tank gain and the capacitance ratio, are presented. The conduction loss is confirmed to be relatively low in DCM because of the essential characteristic of DBCD load. A design procedure is presented and the magnetic integration technique is used for specified transformer leakage inductance. The accuracy of the deduced expressions and design methodologies is verified by simulation and experimental results.

Analysis of the Inactivation Mechanism of Bacteriophage $\varphi\hbox{X}174$ by Atmospheric Pressure Discharge Plasma

Virus inactivation methods using atmospheric pressure discharge plasma have been actively studied these days. However, the predominant factor of the inactivation is not yet well understood. We believe that bacteriophages, which consist of only two components of nucleic acids and coat proteins, are suitable for the study of the inactivation mechanism because their simple structure can enable simple and clear analysis of the mechanisms. In this paper, inactivation of bacteriophage φX174, having some characteristics similar to influenza virus, was investigated using dielectric barrier discharge or corona discharge. In this experimental system using bacteriophage φX174, by transfection, deoxyribonucleic acid (DNA) activity can be separately analyzed from other factors such as coat proteins since it is possible to extract the nucleic acids from the bacteriophage. The coat proteins of the bacteriophage φX174 can be separately analyzed from its DNA as well. Plasma inactivation experiments were made in both wet and dry conditions. As a result, damage was found on both the DNA and the coat proteins of bacteriophage φX174 when it was exposed to the plasma. It was found that the damages given to the coat proteins were more predominant compared with the damages on the DNA.

Effects of Atmospheric DBCD Plasma on Three Kinds of Typical Microorganisms

Dielectric barrier corona discharge (DBCD) is a robust plasma reactor with high efficiency and large scalable area. Nonthermal plasma is generated by DBCD in open condition under atmospheric pressure. Products of plasma are analyzed by using spectroscopy technology. The DBCD plasma is used to treat three kinds of typical microorganisms such as Escherichia coli, Staphylococcus aureus, and Candida albicans. Then, the inactivation effects of the plasma are discussed and compared with our formerly published results of parallel-plate dielectric barrier discharge (DBD) plasma. The results show that the DBCD plasma damages microbe cells by reactive species (RS) and lower pH values, while the parallel-plate DBD plasma works mainly through microdischarge channel and RS. In addition, different cell wall configurations result in different treatment effects.

Effect of BCD Plasma on a Bacteria Cell Membrane

Cell membrane rupture is considered to be one of the probable mechanisms for bacterial inactivation using barrier corona discharge (BCD) plasma. In this paper, the effect of the BCD plasma on the Escherichia coli (E. coli) bacteria cell wall was investigated through two analytical methods; Adenosine-5′-triphosphate (ATP) assay and Atomic Force Microscopy (AFM). The ATP assay results indicate an increase in the ATP content of samples which were exposed to the BCD plasma. This implies the bacteria cell rupture. Moreover, AFM images confirm a serious damage of the bacteria cell wall under the influence of the bactericidal agents of the plasma.

AC Pulse Dielectric Barrier Corona Discharge Over Oil Surfaces: Effect of Oil Temperature

The oil temperature effect on the interaction between plasma caused by high ac pulse barrier corona discharge and dielectric oil film is investigated. The results showed that funnels due to the impact of electric wind or the shock wave generated by streamer discharge occurred more easily under asymmetric negative ac pulse voltages at low oil temperatures but more difficult at high oil temperatures compared with those under asymmetric positive ac pulse voltages. The variation of the funnel diameter with voltage was more obvious under asymmetric positive ac pulse voltages. Oil boiling appeared in the funnel induced by discharge under asymmetric negative ac pulse voltages with high temperatures; thermal flow manifested by localized material transfer existed, and finally, a viscous layer formed in the funnel for oils with elevated temperatures under asymmetric positive ac pulse voltages.

Research on Electrical Characteristics of Dielectric Barrier Discharge and Dielectric Barrier Corona Discharge

The dielectric barrier corona discharge (DBCD) in a wire-cylinder configuration and the dielectric barrier discharge (DBD) in a coaxial cylinder configuration are studied. The discharge current in DBD has higher pulse amplitude than in DBCD. The dissipated power and the gas gap voltage are calculated by analyzing the measured Lissajous figure. DBCD has lower gas gap breakdown voltage. The average electric field is about 10–20 kV/cm in gas gap during DBCD, and is 30–40 kV/cm during DBD. In the positive half cycle the DBCD appears as continuous discharge current mode and in negative half cycle it appears as Trichel pulse mode. Under some conditions DBCD can show homogeneous diffuse discharges mode.

Vacuum-ultraviolet excilamps with excitation by a barrier corona discharge

This paper presents the results of studies of excilamps with excitation by a barrier corona discharge, which is characterized by inhomogeneous broadening of the electric field between the electrodes, one of which is covered by a dielectric. It is established that the radiation efficiency from inert-gas dimers under these excitation conditions reaches 45% at 172 nm and 25% at 146 nm. These studies were used as a basis for creating a radiator complex consisting of sealed xenon-dimer excilamps with a radiation power of up to 120 W, and a wide-aperture compact excilamp with argon pumped through the discharge volume. The radiation power density of the compact excilamp reached 10 mW/cm 2 in the windowless regime.

Generation of the vortex train using plasma barrier discharge actuator

AbstractThe plasma actuator is used to generate periodical train of vortices moving along the surface. For generation the high‐frequency high‐voltage AC is used forming more‐or‐less steady wall‐jet‐like flow by the dielectric barrier discharge or corona discharge. Low‐frequency modulation of the supply voltage is applied to generate vortices. Parameters of the vortex train are studied as function of the generator setting using TR‐PIV technique. The generated flow patterns are to be applied for control of a boundary layer. (© 2011 Wiley‐VCH Verlag GmbH & Co. KGaA, Weinheim)

An Atmospheric-Pressure Glow-Discharge Plasma Jet and Its Application

An atmospheric-pressure glow-discharge plasma jet driven by a transformer of 1 : 500 and an alternating current of 50 Hz is presented. Discharge characteristics are investigated by oscillograph observations, and it is verified no risk of arcing. The stable glow discharge is deemed to benefit from the transformer's inductance. The electric characteristics and the plasma parameters are studied. The jet is employed in CO2 reforming of CH4 to syngas (H2, CO). It brings out higher conversion ability than other plasmas such as dielectric barrier discharge and corona discharge, which is due to its special design and special plasma characteristic.

Degradation of Organic Compounds by Active Species Sprayed in a Dielectric Barrier Corona Discharge System

Investigation was made into the degradation of organic compounds by a dielectric barrier corona discharge (DBCD) system. The DBCD, consisting of a quartz tube, a concentric high voltage electrode and a net wrapped to the external wall (used as ground electrode), was introduced to generate active species which were sprayed into the organic solution through an aerator fixed on the bottom of the tube. The effect of four factors–the discharge voltage, gas flow rate, solution conductivity, and pH of wastewater, on the degradation efficiency of phenol was assessed. The obtained results demonstrated that this process was an effective method for phenol degradation. The degradation rate was enhanced with the increase in power supplied. The degradation efficiency in alkaline conditions was higher than those in acid and neutral conditions. The optimal gas flow rate for phenol degradation in the system was 1.6 L/min, while the solution conductivity had little effect on the degradation.

Physical Modification of Natural Fibers and Thermoplastic Films for Composites — A Review

The article throws light on the physical methods to modify natural fibers to be used in composites. Physical methods in natural fiber processing are used to separate natural fiber bundles into individual filaments and to modify the surface structure of the fibers so as to improve the use of natural fibers in composites. Steam explosion and thermomechanical processes fall in the first category while plasma, dielectric barrier techniques and corona fall in the second. The physical treatments have also been used to modify the thermoplastic polymeric films like polyethylene and polypropylene in a bid to impart reactivity. Reviewing such developments, the areas for further research are suggested.

Repetitively pulsed atmospheric pressure discharge treatment of rough polymer surfaces: I. Humid air discharges

Plasmas generated at atmospheric pressure are used to functionalize the surfaces of polymers by creating new surface-resident chemical groups. The polymers used in textiles and biomedical applications often have non-planar surfaces whose functionalization requires penetration of plasma generated species into sometimes complex surface features. In this regard, the atmospheric pressure plasma treatment of a rough polypropylene surface was computationally investigated using a two-dimensional plasma hydrodynamics model integrated with a surface kinetics model. Repetitively pulsed discharges produced in a dielectric barrier–corona configuration in humid air were considered to affix O. Macroscopic non-uniformities in treatment result from the spatial variations in radical densities which depend on the polarity of the discharge. Microscopic non-uniformities arise due to the higher reactivity of plasma produced species, such as OH radicals, which are consumed before they can diffuse deeper into surface features. The consequences of applied voltage magnitude and polarity, and the relative humidity on discharge dynamics and radical generation leading to surface functionalization, are discussed.

Repetitively pulsed atmospheric pressure discharge treatment of rough polymer surfaces: II. Treatment of micro-beads in He/NH3/H2O and He/O2/H2O mixtures

Plasmas are increasingly being used to functionalize the surface of polymers having complex shapes for biomedical applications such as tissue scaffolds and drug delivering micro-beads. The functionalization often requires affixation of amine (NH2) or O-containing groups. In this paper, results are discussed from a two-dimensional computational investigation of the atmospheric pressure plasma functionalization of non-planar and porous surfaces of polypropylene with NHx and O-containing groups. For the former, the discharge is sustained in He/NH3/H2O mixtures in a dielectric barrier–corona configuration. Significant microscopic non-uniformities arise due to competing pathways for reactive gas phase radicals such as OH and NH2, and on the surface by the availability of OH to initiate amine attachment. The treatment of inside surfaces of porous polymer micro-beads placed on an electrode is particularly sensitive to view angles to the discharge and pore size, and is ultimately controlled by the relative rates of radical transport and surface reactions deep into the pores. The functionalization of micro-beads suspended in He/O2/H2O discharges is rapid with comparable treatment of the outer and interior surfaces, but varies with the location of the micro-bead in the discharge volume.

High voltage breakdown in an inductively coupled ion source

An inductively coupled plasma source, designed for ion beam applications, is allowed to float up to several kilovolt positive. If one side of the radio frequency (rf) antenna is grounded and the dielectric source tube and the surrounding air are allowed to reach a threshold temperature corona breakdown at the rf antenna occurs. The experiments presented here show that a dc corona can be ignited with the presence of a dielectric barrier, which normally precludes dc breakdown. The formation of a negative barrier corona initiates a transition to a continuous arc from the rf antenna to the source tube. It is suggested that the onset of the first filaments heat the dielectric locally, such that the dielectric strength drops. DC current channels are then formed in the source tube, allowing a resistive corona with continuous arcs to exist.

Efficient decomposition of NO by ammonia radical-injection method using an intermittent dielectric barrier discharge

Although many NO decomposition systems have been developed using plasmas such as dielectric barrier discharges (DBDs), corona discharges, surface discharges, glow discharges, and microwave discharges, the present system is unique on the viewpoint of the use of an intermittent one-cycle sinusoidal power source to generate DBD plasma. There are several features of the system: (1) easy control of the electric power consumed in the DBD plasma, and (2) DBD-plasma generation used only for the production of ammonia radicals. The system employs a radical injection system, where the radicals are produced in a separate discharge chamber, called radical injector, from NO flow field. This enables an efficient production of ammonia radicals being appropriate for DeNOx. It is shown from the temperature dependence of NO removal (DeNOx) characteristics that the present system is a low-temperature DeNOx system compared to a conventional thermal DeNOx system, and NO decomposition is performed over a wide range of gas temperature containing NO. Surveying parametric characteristics of DeNOx, the energy efficiency is improved by a factor of 30% compared to the previously obtained result.